Order And Disorder In Crystalline Ice Explained (Physics)

A new theoretical model enlightens the structure and the electrical properties of pure and doped ice.

A fascinating substance with unique properties, ice has intrigued humans since time immemorial. Unlike most other materials, ice at very low temperature is not as ordered as it could be. A collaboration between SISSA, ICTP and the Institute of Physics Rosario (IFIR-UNR), with the support of CNR-IOM, made new theoretical inroads on the reasons why this happens and on the way in which some of the missing order can be recovered. In that ordered state the team of scientists have described a relatively obscure and yet fundamental property of very low temperature ice, ferroelectricity. The results, published in PNAS, are likely to extend to ice surfaces, a possibility that could be relevant to the agglomeration of ice particles in interstellar space.

String of proton-ordered water molecules caught in motion © Lasave, Koval, Laio, Tosatti

“In an ideally ordered piece of ice the hydrogen atoms of each water molecule should point in the same direction, like soldiers in a platoon looking in front of them,” explains Alessandro Laio, physicist of SISSA and ICTP. “If that was the case, ice would exhibit a macroscopic electric polarization ? it would be ferroelectric. Instead, water molecules in ice, even at very low temperature, behave like unruly soldiers, and all look in different directions.”

This anomalous behaviour, discovered experimentally in the 1930s, was immediately and famously explained by Linus Pauling: the lack of discipline is an effect of the ‘ice rule’ constraint ? every oxygen atom should at any moment possess two and only two protons to make it H2O. The difficult kinetics created by that constraint causes the ordering process to become infinitely slow, as in a platoon where each soldier had four neighbours and had to keep two hands on the shoulders of two of them.

“Were it not for impurities or defects, which turned out to play a revealing role, one would still today not know whether proton order and ferroelectricity of bulk crystalline ice is a real possibility or a figment of the imagination, since neither experiments nor simulations could overcome the ice rule-generated kinetic slowdown,” points out Erio Tosatti, physicist of SISSA, ICTP and CNR-IOM Democritos.

Impurities, such as one KOH replacing H2O, are in fact known to allow the ordering process to nucleate and ice to turn ordered and ferroelectric at very low temperature, although only partly and sluggishly. Once again, the ‘ice rule’ was suspected to be behind the sluggishness of this process, but exactly how that worked was not really known.

Together with Jorge Lasave and Sergio Koval of the IFIR-UNR in Argentina, both of them ICTP associate members, Alessandro Laio and Erio Tosatti designed a theoretical model and a strategy to explain the behaviour of both pure and doped ice.

“According to this model,” the scientists explain, “once an impurity is introduced inside an initial non-equilibrium low temperature disordered state, it acts as a seed for the ordered phase, but in a peculiar manner: not all the ‘soldiers’ around the impurity start looking in the correct direction, but only those in front or behind the impurity. Thus, at the end of the process only a string of soldiers inside the platoon will become ordered.” This highly atypical process has many of the characteristics that can explain the sluggish and incomplete onset of ferroelectric order in real doped ice.

“Although the study is restricted for now to bulk ice,” Tosatti and Laio conclude, “the mechanism highlighted is likely to extend to ice surfaces, where strings of ordered protons could nucleate at low temperatures, explaining a long known small amount of local ferroelectric polarization, a phenomenon also mentioned as possibly relevant to the agglomeration of ice particles in interstellar space.”

Paper: https://www.pnas.org/content/pnas/
118/1/e2018837118.full.pdf

Provided by SISSA

Researchers Publish Review Article on the Physics Of Interacting Particles (Physics)

Scientific articles in the field of physics are mostly very short and deal with a very restricted topic. A remarkable exception to this is an article published recently by physicists from the Universities of Münster and Düsseldorf. The article is 127 pages long, cites a total of 1075 sources and deals with a wide range of branches of physics – from biophysics to quantum mechanics.

The authors of the review article: The scientists Michael te Vrugt and Raphael Wittkowski from Münster University and their colleague Hartmut Löwen from Düsseldorf University (from left).
© WWU – Melissa Pernice / HHU – Christoph Kawan

The article is a so-called review article and was written by physicists Michael te Vrugt and Prof. Raphael Wittkowski from the Institute of Theoretical Physics and the Center for Soft Nanoscience at the University of Münster, together with Prof. Hartmut Löwen from the Institute for Theoretical Physics II at the University of Düsseldorf. The aim of such review articles is to provide an introduction to a certain subject area and to summarize and evaluate the current state of research in this area for the benefit of other researchers. “In our case we deal with a theory used in very many areas – the so-called dynamical density functional theory (DDFT),” explains last author Raphael Wittkowski. “Since we deal with all aspects of the subject, the article turned out to be very long and wide-ranging.”

Time axis showing the number of publications relating to dynamical density functional theory. © M. te Vrugt et al.

DDFT is a method for describing systems consisting of a large number of interacting particles such as are found in liquids, for example. Understanding these systems is important in numerous fields of research such as chemistry, solid state physics or biophysics. This in turn leads to a large variety of applications for DDFT, for example in materials science and biology. “DDFT and related methods have been developed and applied by a number of researchers in a variety of contexts,” says lead author Michael te Vrugt. “We investigated which approaches there are and how they are connected – and for this purpose we needed to do a lot of work acting as historians and detectives,” he adds.

The article has been published in the journal “Advances in Physics”, which has an impact factor of 30.91 – making it the most important journal in the field of condensed matter physics. It only publishes four to six articles per year. The first article on DDFT, written by Robert Evans, was also published in “Advances in Physics”, in 1979. “This makes it especially gratifying that our review has also been published in this journal,” says secondary author Hartmut Löwen. “It deals with all the important theoretical aspects and fields of application of DDFT and will probably become a standard work in our field of research.”

Funding

The Wittkowski working group is being funded by the German Research Foundation DFG (WI 4170/3-1). The Löwen working group is also receiving financial support from the DFG (LO 418/25-1).

References: Michael te Vrugt, Hartmut Löwen & Raphael Wittkowski (2020) Classicaldynamical density functional theory: from fundamentals to applications, Advances in Physics, 69:2,121-247, https://www.tandfonline.com/doi/full/10.1080/00018732.2020.1854965 DOI: 10.1080/00018732.2020.1854965

Provided by WMU Munster

UCLA Scientists Develop High-throughput Mitochondria Transfer Device (Medicine)

Method will help researchers better understand mitochondrial DNA diseases.

Scientists from the UCLA Jonsson Comprehensive Cancer have developed a simple, high-throughput method for transferring isolated mitochondria and their associated mitochondrial DNA into mammalian cells. This approach enables researchers to tailor a key genetic component of cells, to study and potentially treat debilitating diseases such as cancer, diabetes and metabolic disorders.

Dr. Michael Teitell is director of the UCLA Jonsson Comprehensive Cancer Center. © UCLA

A study, published online in the journal Cell Reports, describes how the new UCLA-developed device, called MitoPunch, transfers mitochondria into 100,000 or more recipient cells simultaneously, which is a significant improvement from existing mitochondrial transfer technologies. The device is part of the continued effort by UCLA scientists to understand mutations in mitochondrial DNA by developing controlled, manipulative approaches that improve the function of human cells or model human mitochondrial diseases better.

“The ability to generate cells with desired mitochondrial DNA sequences is powerful for studying how genomes in the mitochondria and nucleus interact to regulate cell functions, which can be critical for understanding and potentially treating diseases in patients,” said Alexander Sercel, a doctoral candidate at the David Geffen School of Medicine at UCLA and co-first author of the study.

Mitochondria, often known as the ‘powerplant’ of a cell, are inherited from a person’s mother. They rely on the integrity of the mitochondrial DNA to perform their essential functions. Inherited or acquired mutations of the mitochondrial DNA can significantly impair energy production and may result in debilitating diseases.

Technologies for manipulating mitochondrial DNA lag behind advances for manipulating DNA in the nucleus of a cell and could potentially help scientists develop disease models and regenerative therapies for disorders caused by these mutations. Current approaches, however, are limited and complex, and for the most part can only deliver mitochondria with desired mitochondrial DNA sequences into a limited number and variety of cells.

The MitoPunch device is simple to operate and allows for consistent mitochondrial transfers from a wide range of mitochondria isolated from different donor cell types into a multitude of recipient cell types, even for non-human species, including for cells isolated from mice.

 “What sets MitoPunch apart from other technologies is an ability to engineer non-immortal, non-malignant cells, such as human skin cells, to generate unique mitochondrial DNA-nuclear genome combinations,” said co-first author Alexander Patananan, a UCLA postdoctoral scholar, who now works at Amgen. “This advance allowed us to study the impact of specific mitochondrial DNA sequences on cell functions by also enabling the reprogramming of these cells into induced pluripotent stem cells that were then differentiated into functioning fat, cartilage, and bone cells.”

MitoPunch was created in the labs of Dr. Michael Teitell, director of the Jonsson Cancer Center and professor of pathology and laboratory medicine, Pei-Yu (Eric) Chiou, professor of mechanical and aerospace engineering at the UCLA Henry Samueli School of Engineering and Applied Science, and Ting-Hsiang Wu, from ImmunityBio, Inc., Culver City, CA.

MitoPunch builds upon prior technology and a device called a photothermal nanoblade, which the team developed in 2016. But unlike the photothermal nanoblade, which requires sophisticated lasers and optical systems to operate, MitoPunch works by using pressure to propel an isolated mitochondrial suspension through a porous membrane coated with cells. The researchers propose that this applied pressure gradient creates the ability to puncture cell membranes at discrete locations, allowing the mitochondria direct entry into recipient cells, followed by cell membrane repair.

“We knew when we first created the photothermal nanoblade that we would need a higher-throughput, simpler to use system that is more accessible for other laboratories to assemble and operate,” said Teitell, who is also the chief of the division of pediatric and developmental pathology and a member of the UCLA Broad Stem Cell Research Center. “This new device is very efficient and allows researchers to study the mitochondrial genome in a simple way — swapping it from one cell into another — which can be used to uncover the basic biology that governs a broad range of cell functions and could, one day, offer hope for treating mitochondrial DNA diseases.”

The research was supported by the National Institutes of Health, by the American Heart Association and by the Human Performance and Biosystems division of the US Air Force Office of Scientific Research.

Reference: Alexander N. Patananan et al, Pressure-Driven Mitochondrial Transfer Pipeline Generates Mammalian Cells of Desired Genetic Combinations and Fates, Cell Reports (2020). http://dx.doi.org/10.1016/j.celrep.2020.108562

Provided by UCLA

The Puzzle of Nonhost Resistance: Why Do Pathogens Harm Some Plants But Not Others? (Botany)

People have puzzled for years why pathogen Phytophthora infestens causes the devastating late blight disease, source of the Irish Potato famine, on potatoes, but has no effect at all on plants like apple or cucumber. How are apple trees and cucumber plants able to completely shake off this devastating pathogen? Agricultural scientists have wondered for years: if this resistance is so complete and persists over so many generations, is there some way we could transfer it to susceptible plants like wheat and thereby stop disease?

Ralph Panstruga & Matthew Moscou © Ralph Panstruga & Matthew Moscou

Why is it so important to determine the molecular basis of nonhost resistance?

There are many examples of plants that are susceptible to one pathogen but able to resist another closely related pathogen. By uncovering the mechanism behind resistance, we can obtain a deeper understanding of the plant immune system and can also uncover previously unknown aspects of immune signaling and regulation, which can help scientists improve resistance against a broader spectrum of pathogens.

This question has always been important as pathogens are a consistent threat to agriculture, limiting how much food is produced and where crops can be grown. Scientists continue to learn ways to reduce the impact of disease, through the development of pesticides, implementing new practices in the field, and breeding crops with enhanced resistance.

However, the modern world inadvertently undermines these efforts in a number of ways. Globalization and increased movement have contributed to the spread of pathogens into new environments. A prominent example is the recent emergence of wheat blast disease caused by the fungus Magnaporthe oryzae, which for a long time was unable to colonize wheat.

“The field of nonhost resistance sets out to identify novel ways to engineer resistance to these plant pathogens, guided by approaches that already exist in nature,” explained Matthew Moscou, a scientist at The Sainsbury Laboratory in Norwich, United Kingdom. “This question is fundamental to understanding why some plants get infected by a particular pathogen and others don´t, and, vice versa, why a given pathogen can only successfully colonize a limited number of plant species, which collectively form its host range.”

Nonhost resistance is a gradual phenomenon that is modulated by various exogenous factors. The central part of the figure depicts the continuum between nonhost and host plants, with several intermediate forms possible. © Ralph Panstruga and Matthew J. Moscou

What do we know about nonhost resistance?

Scientists have learned that nonhost resistance is a feature controlled by many genes and largely governed by the characteristic attributes of a given plant-pathogen constellation. Pre-existing and induced physical barriers, such as the plant cuticle, and the secretion of antimicrobial molecules are often key factors in nonhost resistance. More recently scientists have recognized the interplay of host NLR-type immune sensors and secreted pathogen effector proteins as another important determinant of nonhost resistance.

What don’t we know about nonhost resistance?

“While the contribution of microbial commensals (microbes that naturally inhabit plant organs without causing any harm) to plant immunity has emerged during the past few years, their explicit role in nonhost resistance has not been demonstrated yet”, said Ralph Panstruga, a scientist at RWTH Aachen University in Germany. “Our knowledge on nonhost resistance largely relies on findings obtained in a handful of (model) angiosperm plant species that are genetically very tractable. We do not know yet to what extent these insights can be generalized, especially with respect to non-angiosperms.”

While there is a lot we don’t know about nonhost resistance, recent advances in technology, such as DNA sequencing methods, will make it easier for scientists to learn more. As for understanding the contribution of microbial commensals, scientists have recently been able to explore this aspect through reconstitution experiments with synthetic microbial communities in combination with germ-free plant systems. These tools were only recently established for some model plant species and are not yet available for many agriculturally important crops.

What can come from answering this question?

Learning more about nonhost resistance will help scientists better appreciate that susceptibility and resistance are the extreme outcomes of interactions between plants and pathogens, with all kinds of intermediate forms possible. Scientists may also discover undiscovered of plant pathogens on some species, which will enhance disease control strategies. Answering this question will also help scientists further comprehend whether microbial commensals contribute to resistance, which could form the basis for future plant protection measures. Finally, these insights will complete our picture of the plant immune system.

For the full review, read “What is the Molecular Basis of Nonhost Resistance?” published in the November issue of the MPMI journal. This article is the first in a series of ten reviews exploring the top 10 unanswered questions in molecular plant-microbe interactions, which came out of a crowdsourcing initiative spearheaded by the MPMI journal’s editorial board at the 2019 International Congress on Molecular Plant-Microbe Interactions in Glasgow, Scotland.

When meeting attendees Panstruga and Moscou heard about the quest to identify the top 10 unanswered questions in MPMI, they were immediately fascinated. When they saw the final list, they were drawn to the question about nonhost resistance, a plant defense that provides immunity to all members of a plant species against a microorganism that is harmful to other plant species.

“Since we both have published expertise in the area of nonhost resistance, it was somewhat self-evident that we could contribute with a review article to this relevant question,” said Panstruga. “We felt for quite some time that some concepts and terms in the field are ambiguous and possibly misleading, and that it would be just the right time to sum up the present knowledge, but also to clarify a few aspects and to raise a few fresh ideas.”

References: Ralph Panstruga and Matthew J. Moscou, “What is the Molecular Basis of Nonhost Resistance?”, APS, Oct 2020. https://doi.org/10.1094/MPMI-06-20-0161-CR

Provided by American Phytopathological Society

A Single Gene ‘Invented’ Haemoglobin Several Times (Biology)

Thanks to the marine worm Platynereis dumerilii, an animal whose genes have evolved very slowly, scientists from CNRS, Université de Paris and Sorbonne Université, in association with others at the University of Saint Petersburg and the University of Rio de Janeiro, have shown that while haemoglobin appeared independently in several species, it actually descends from a single gene transmitted to all by their last common ancestor. These findings were published on 29 December 2020 in BMC Evolutionary Biology.

The Platynereis dumerilii vascular system in three segments © Song et al. / BMC Evolutionary Biology

Having red blood is not peculiar to humans or mammals. This colour comes from haemoglobin, a complex protein specialized in transporting the oxygen found in the circulatory system of vertebrates, but also in annelids (a worm family whose most famous members are earthworms), molluscs (especially pond snails) and crustaceans (such as daphnia or ‘water fleas’). It was thought that for haemoglobin to have appeared in such diverse species, it must have been ‘invented’ several times during evolution. But recent research has shown that all of these haemoglobins born ‘independently’ actually derive from a single ancestral gene.

Researchers from the Institut Jacques Monod (CNRS/Université de Paris), the Laboratoire Matière et Systèmes Complexes (CNRS/Université de Paris), the Station Biologique de Roscoff (CNRS/Sorbonne Université), the Universities of Saint Petersburg (Russia) and Rio de Janeiro (Brazil), conducted this research on Platynereis dumerilii, a small marine worm with red blood.

It is considered to be an animal that evolved slowly, because its genetic characteristics are close to those of the marine ancestor of most animals, Urbilateria(1). Studying these worms by comparing them with other species with red blood has helped in tracing back to the origins of haemoglobins.

The research focused on the broad family to which haemoglobins belong: globins, proteins present in almost all living beings that ‘store’ gases like oxygen and nitric oxide. But globins usually act inside the cells because they do not circulate in the blood like haemoglobin.

This work shows that in all species with red blood, it is the same gene that makes a globin called ‘cytoglobin’ that independently evolved to become a haemoglobin-encoding gene. This new circulating molecule made oxygen transport more efficient in their ancestors, who became larger and more active.

Scientists now want to change scale and continue this work by studying when and how the different specialized cells of bilaterian vascular systems emerged.

(1) Urbilateria is the last common ancestor of bilaterians, i.e. animals with bilateral (left-right) symmetry and complex organs, apart from species with simpler organization such as sponges and jellyfish.

Reference: Solène Song, Viktor Starunov, Xavier Bailly, Christine Ruta, Pierre Kerner, Annemiek J. M. Cornelissen, Guillaume Balavoine. Globins in the marine annelid Platynereis dumerilii shed new light on hemoglobin evolution in bilaterians. BMC Evolutionary Biology, 2020; 20 (1) DOI: 10.1186/s12862-020-01714-4 https://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-020-01714-4

Provided by CNRS

In Plants, Channel Set The Rhythm (Botany)

Although plants are anchored to the ground, they spend most of their lifetime swinging in the wind. Now Tran and colleagues found that, like animals, plants have ‘molecular switches’ on the surface of their cells that transduce a mechanical signal into an electrical one in milliseconds.

Plants are endowed with mechanosensitive channels such as MSL that transduce mechanical oscillations into electrical signals. In static condition, the cell membrane of the model plant Arabidopsis thaliana is hardly solicited, and the MSL10 ‘switch’ shows little activity (left-hand side). When the membrane is subjected to an oscillatory pressure mimicking the effect of the wind, the switch becomes more active (oscillation, right-hand side). This is shown schematically on the diagram in the bottom right of the figure. © Jean-Marie Frachisse and Daniel Tran, Institut de Biologie Integrative de la Cellule (CNRS/Université Paris-Saclay).

In animals, sound vibrations activate ‘molecular switches’ located in the ear. While, they have found that in plants, rapid oscillations of stems and leaves due to wind may activate these ‘switches’ very effectively. They could allow plants to ‘listen’ to the wind. This is a key advantage in preparing them for storms, by modulating their growth. This work was published in PNAS on December 28, 2020.

References: Daniel Tran, Tiffanie Girault, Marjorie Guichard, Sébastien Thomine, Nathalie Leblanc-Fournier, Bruno Moulia, Emmanuel de Langre, Jean-Marc Allain, Jean-Marie Frachisse, “Cellular transduction of mechanical oscillations in plants by the plasma-membrane mechanosensitive channel MSL10”, PNAS, 28 December 2020. DOI: 10.1073/pnas.1919402118 https://www.pnas.org/content/118/1/e1919402118

Provided by CNRS

Sugars Influence Cell-to-surface Adhesion (Biology)

Biotechnologists measure the forces with which algae cells adhere to surfaces and move on them.

How can cells adhere to surfaces and move on them? This is a question which was investigated by an international team of researchers headed by Prof. Michael Hippler from the University of Münster and Prof. Kaiyao Huang from the Institute of Hydrobiology (Chinese Academy of Sciences, Wuhan, China). The researchers used the green alga Chlamydomonas reinhardtii as their model organism. They manipulated the alga by altering the sugar modifications in proteins on the cell surface. As a result, they were able to alter the cellular surface adhesion, also known as adhesion force. The results have now been published in the open access scientific journal “eLife”.

Using TIRF microscopy, Flagella-mediated adhesion can be visualized and analysed.
© Lara Hoepfner

Background and methodology

In order to move, the green alga has two thread-like flagella on its cell surface. The alga actually uses these flagella for swimming, but it can also use them to adhere to surfaces and glide along them. The researchers now wanted to find out how movement and adhesion on the part of the alga can be manipulated. “We discovered that proteins on cell surfaces that are involved in this process are modified by certain sugars. If these sugar chains on the proteins are altered, this enables their properties to be altered,” explains Michael Hippler from the Institute of the Biology and Biotechnology of Plants at Münster University. Experts then describe such proteins as being N-glycosylated – a modification in which carbohydrates are docked onto amino groups. Alterations to these sugar modifications by genetically manipulating the algae showed that the adhesion force of the algae and, as a result, any adhesion to surfaces were reduced. At the same time, there was no change in the cells gliding on the surface. The much-reduced force with which the mutants adhere to surfaces is therefore still sufficient, under laboratory conditions, to enable gliding to take place.

Flagella-mediated adhesion and gliding by Chlamydomonas reinhardtii (green alga) on a solid surface (top). Using TIRF microscopy, these dynamics can be visualized and analysed (bottom). © Lara Hoepfner

In order to study these processes, the researchers first used so-called insertional mutagenesis and the CRISPR/Cas9 method to deactivate genes which encode enzymes relevant to the N-glycosylation process. “The next step was to analyse the sugar modifications of these genetically altered algae strains using mass spectrometry methods,” says Michael Hippler, explaining the team’s approach. In order to visualise the cell-gliding, the researchers used a special method of optical microscopy – total internal reflection fluorescence microscopy (TIRF). This method is frequently used to carry out examinations of structures which are located very close to a surface. For this purpose, a fluorescent protein was expressed in the flagella of the algae in order to make the flagella and the cell-gliding visible.

In order to measure how much force was used in adhering the individual cells to the surface, atomic force microscopy was used and micropipette adhesion measurements were undertaken in collaboration with groups at the University of Liverpool (UK) and the Max Planck Institute of Dynamics and Self-Organization in Göttingen. “This enabled us to verify that adhesion forces in the nanometre range are reduced by altering the protein sugar modifications,” adds Kaiyao Huang.

The two flagella on the green alga resemble for example not only the flagella of sperm but also other movable flagella. These are usually called ‘cilia’ and are also found in the human body – for example in the respiratory tracts. “If we transfer our findings to human cells, sugar-modified proteins could be used to change the interaction of sperm or cilia with all sorts of surfaces,” say Kaiyao Huang and Michael Hippler.

Research participants

Besides researchers from the University of Münster, scientists from Berlin’s Humboldt University, the Universities of Wuhan (China) and Liverpool (England) and the Max Planck Institute of Dynamics and Self-Organization in Göttingen contributed to the study.

Funding

The study received financial support from the German Research Foundation (DFG) and the National Nature Science Foundation of China, as well as from the Royal Society and the Biotechnology and Biological Sciences Research Council in the UK.

References: Nannan Xu, Anne Oltmanns, Longsheng Zhao, Antoine Girot, Marzieh Karimi, Lara Hoepfner, Simon Kelterborn, Martin Scholz, Julia Beißel, Peter Hegemann, Oliver Bäumchen, Lu-Ning Liu, Kaiyao Huang, Michael Hippler (2020). Altered N-glycan composition impacts flagella mediated adhesion in Chlamydomonas reinhardtii. eLife. DOI: 10.1101/2020.05.18.102624 https://elifesciences.org/articles/58805

Provided by WMU Munster

Electrons Hop To It on Twisted Molecular Wires (Chemistry)

Scientists at Osaka University devise a method to improve the conductivity of molecular wires by intentionally adding periodic twists to the conjugated chains, which may lead to sophisticated and more environmentally friendly electronics.

Researchers at Osaka University synthesized twisted molecular wires just one molecule thick that can conduct electricity with less resistance compared with previous devices. This work may lead to carbon-based electronic devices that require fewer toxic materials or harsh processing methods.

Concept and chemical structure of periodically twisted molecular wires. © Osaka University

Organic conductors, which are carbon-based materials that can conduct electricity, are an exciting new technology. Compared with conventional silicon electronics, organic conductors can be synthesized more easily, and can even be made into molecular wires. However, these structures suffer from reduced electrical conductivity, which prevents them from being used in consumer devices. Now, a team of researchers from The Institute of Scientific and Industrial Research and the Graduate School of Engineering Science at Osaka University has developed a new kind of molecular wire made from oligothiophene molecules with periodic twists that can carry electric current with less resistance.

Molecular wires are composed by several-nanometer-scale long molecules that have alternating single and double chemical bonds. Orbitals, which are states that electrons can occupy around an atom or molecule, can be localized or extended in space. In this case, the pi orbitals from individual atoms overlap to form large “islands” that electrons can hop between. Because electrons can hop most efficiently between levels that are close in energy, fluctuations in the polymer chain can create energy barriers. “The mobility of charges, and thus the overall conductivity of the molecular wire, can be improved if the charge mobility can be improved by suppressing such fluctuations,” first author Yutaka Ie says.

The overlap of pi orbitals is very sensitive to the rotation of the molecule. Adjacent segments of the molecule that are aligned in the same plane form one large hopping site. By purposely adding twists to the chain, the molecule is broken into nanometer-sized sites, but because they are close in energy, the electrons can hop easily between them. This was accomplished by inserting a 3,3′-dihexyl-2,2′-bithiophene unit after every stretch of 6 or 8 oligothiophene units.

The team found that, overall, creating smaller islands that are closer in energy maximized the conductivity. They also measured how temperature affects the conductivity, and showed that it was indeed based on electron hopping. “Our work is applicable to single-molecule wires, as well as organic electronics in general,” senior author Yoshikazu Tada says. This research may lead to improvements in conductivity that will allow nanowires to become incorporated into a wide array of electronics, such as tablets or computers.

Reference: Yutaka Ie, Yuji Okamoto, Takuya Inoue, Takuji Seo, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada, and Yoshio Aso, “Improving Intramolecular Hopping Charge Transport via Periodical Segmentation of π-Conjugation in a Molecule”, J. Am. Chem. Soc. 2020. https://pubs.acs.org/doi/10.1021/jacs.0c10560
https://doi.org/10.1021/jacs.0c10560

Provided by Osaka University

Flag Leaves Could Help Top Off Photosynthetic Performance in Rice (Botany)

The flag leaf is the last to emerge, indicating the transition from crop growth to grain production. Photosynthesis in this leaf provides the majority of the carbohydrates needed for grain filling—so it is the most important leaf for yield potential. A team from the University of Illinois and the International Rice Research Institute (IRRI) found that some flag leaves of different varieties of rice transform light and carbon dioxide into carbohydrates better than others. This finding could potentially open new opportunities for breeding higher yielding rice varieties.

A team from the University of Illinois and the International Rice Research Institute explored flag leaf induction–the process in which photosynthesis “starts up” again after a transition from low to high light–in six varieties of rice. © Liana Acevedo-Siaca/RIPE project

Published in the Journal of Experimental Botany, this study explores flag leaf induction—which is the process that the leaf goes through to “start up” photosynthesis again after a transition from low to high light. This is important because the wind, clouds, and movement of the sun across the sky cause frequent fluctuations in light levels. How quickly photosynthesis adjusts to these changes has a major influence on productivity. 

For the first time, these researchers revealed considerable differences between rice varieties in the ability of flag leaves to adjust to fluctuating light. They also showed that the ability to adjust differs between the flag leaf and leaves formed before flowering. Six rice varieties chosen to represent the breadth of genetic variation across a diverse collection of more than 3000 were analyzed as a first step in establishing if there was variation in ability to cope with fluctuations in light. 

In this study, they discovered the flag leaf of one rice variety that began photosynthesizing nearly twice (185%) as fast as the slowest. Another top-performing flag leaf fixed 152% more sugar. They also found large differences (77%) in how much water the plant’s flag leaves exchanged for the carbon dioxide that fuels photosynthesis. Additionally, they found that water-use efficiency in flag leaves correlated with water-use efficiency earlier in development of these rice varieties, suggesting that water-use efficiency in dynamic conditions could be screened for at younger stages of rice development. 

“What’s more, we found no correlation between the flag leaf and other leaves on the plant, aside from water-use efficiency, which indicates that both kinds of leaves may need to be optimized for induction,” said Stephen Long, Illinois’ Ikenberry Endowed University Chair of Crop Sciences and Plant Biology. “While this means more work for plant scientists and breeders, it also means more opportunities to improve the plant’s photosynthetic efficiency and water use. Improving water use is of increasing importance, as agriculture already accounts for over 70% of human water use, and rice is perhaps the largest single part of this.”

Confirming their previous study in New Phytologist, they found no correlation between data collected in fluctuating and steady-state conditions, where the rice plants were exposed to constant high light levels. This finding adds to a growing consensus that researchers should move away from research dependent on steady-state measurements. 

“We’re realizing the need for our experiments to more accurately reflect the reality that these plants experience out the field,” said first-author Liana Acevedo-Siaca, a postdoctoral researcher at Illinois. “We need to focus our efforts on capturing the dynamic conditions so we can improve crops to be productive in the real world, not laboratories.” 

This work is part of Realizing Increased Photosynthetic Efficiency (RIPE), a project that aims to improve photosynthesis to equip farmers worldwide with higher-yielding crops to ensure everyone has enough food to lead a healthy and productive life. RIPE is sponsored by the Bill & Melinda Gates Foundation, the U.S. Foundation for Food & Agriculture Research, and the U.K. Foreign, Commonwealth & Development Office who are committed to ensuring Global Access and making the project’s technologies available to the farmers who need them the most.

Reference: Liana G. Acevedo-Siaca, Robert Coe, W. Paul Quick, Stephen P. Long, “Variation between rice accessions in photosynthetic induction in flag leaves and underlying mechanisms”, Journal of Experimental Botany, 2020. https://doi.org/10.1093/jxb/eraa520 https://ripe.illinois.edu/publications/variation-between-rice-accessions-photosynthetic-induction-flag-leaves-and-underlying

Provided by University of Illinois